Nuclear broadening effects on hard prompt photons at CERN-SPS and BNL-RHIC energies

Abstract

We discuss nuclear broadening of the intrinsic transverse momentum of partons in the initial state, and its influence on the p t distribution of prompt photons.Comparing to WA98 data from Pb+Pb collisions at √ s = 17.4A GeV we find evidence for the presence of nuclear broadening at high p t in this hard process. Below p t ∼ 2.7 GeV the photon distribution is due to small momentum transfer processes. At RHIC energy, √ s = 200A GeV, the effect of intrinsic transverse momentum on the spectrum of prompt photons is less prominent. Below p t = 2 − 3 GeV the contribution from large momentum transfers flattens out, and we expect that region to be dominated by soft contributions.